Organometallic iridium complex, light-emitting element, light-emitting device, and lighting device

ABSTRACT

In the formula, R1 to R3 separately represent an alkyl group having 1 to 6 carbon atoms, a phenyl group, or a phenyl group having an alkyl group having 1 to 6 carbon atoms as a substituent.

This application is a continuation of copending U.S. application Ser.No. 14/300,695, filed on Jun. 10, 2014 which is incorporated herein byreference.

TECHNICAL FIELD

One embodiment of the present invention relates to an organometalliciridium complex, particularly, to an organometallic iridium complex thatis capable of converting a triplet excited state into luminescence. Inaddition, one embodiment of the present invention relates to alight-emitting element, a light-emitting device, and a lighting devicethat include the organometallic iridium complex.

BACKGROUND ART

Organic compounds are brought into an excited state by absorbing light.Through this excited state, various reactions (photochemical reactions)are caused in some cases, or luminescence is generated in some cases.Therefore, the organic compounds have a wide range of applications.

As one example of the photochemical reactions, a reaction of singletoxygen with an unsaturated organic molecule (oxygen addition) is known.Since the ground state of an oxygen molecule is a triplet state, oxygenin a singlet state (singlet oxygen) is not generated by directphotoexcitation. However, in the presence of another triplet excitedmolecule, singlet oxygen is generated to cause an oxygen additionreaction. In this case, a compound capable of forming the tripletexcited molecule is referred to as a photosensitizer.

As described above, for generation of singlet oxygen, a photosensitizercapable of forming a triplet excited molecule by photoexcitation isneeded. However, the ground state of an ordinary organic compound is asinglet state; therefore, photoexcitation to a triplet excited state isforbidden transition and generation of a triplet excited molecule isdifficult. A compound that can easily cause intersystem crossing fromthe singlet excited state to the triplet excited state (or a compoundthat allows the forbidden transition of photoexcitation directly to thetriplet excited state) is thus required as such a photosensitizer. Inother words, such a compound can be used as the photosensitizer and isuseful.

Such a compound often exhibits phosphorescence. Phosphorescence refersto luminescence generated by transition between different energies inmultiplicity. In an ordinary organic compound, phosphorescence refers toluminescence generated in returning from the triplet excited state tothe singlet ground state (in contrast, fluorescence refers toluminescence in returning from the singlet excited state to the singletground state). Application fields of a compound capable of exhibitingphosphorescence, that is, a compound capable of converting the tripletexcited state into luminescence (hereinafter, referred to as aphosphorescent compound), include a light-emitting element including anorganic compound as a light-emitting substance.

This light-emitting element has a simple structure in which alight-emitting layer including an organic compound that is alight-emitting substance is provided between electrodes. Thislight-emitting element attracts attention as a next-generation flatpanel display element in terms of characteristics such as being thin andlight in weight, high speed response, and direct current low voltagedriving. A display device including this light-emitting element issuperior in contrast, image quality, and has wide viewing angle.

The emission mechanism of a light-emitting element in which an organiccompound is used as a light-emitting substance is a carrier injectiontype. That is, by applying voltage with a light-emitting layerinterposed between electrodes, electrons and holes injected from theelectrodes recombine to make the light-emitting substance excited, andlight is emitted when the excited state returns to a ground state. As inthe case of photoexcitation described above, types of the excited stateinclude a singlet excited state (S*) and a triplet excited state (T*).The statistical generation ratio thereof in the light-emitting elementis S*:T*=1:3.

In a compound which converts a singlet excited state into light emission(hereinafter referred to as a fluorescent compound), light emission froma triplet excited state (phosphorescence) is not observed at a roomtemperature but only light emission from a singlet excited state(fluorescence) is observed. Therefore, the internal quantum efficiency(the ratio of the number of generated photons to the number of injectedcarriers) of a light-emitting element including the fluorescent compoundis assumed to have a theoretical limit of 25%, on the basis ofS*:T*=1:3.

In contrast, in the case of a light-emitting element including thephosphorescent compound described above, the internal quantum efficiencythereof can be improved to 75% to 100% in theory; namely, the emissionefficiency thereof can be 3 to 4 times as much as that of thelight-emitting element including a fluorescent compound. For thisreason, light-emitting elements using a phosphorescent compound havebeen recently under active development so that light-emitting elementswith high efficiency can be achieved. As the phosphorescent compound, anorganometallic complex that contains iridium or the like as a centralmetal has particularly attracted attention because of its highphosphorescence quantum yield (see, for example, Patent Document 1,Patent Document 2, and Patent Document 3).

REFERENCE Patent Document

-   Patent Document 1: Japanese Published Patent Application No.    2007-137872-   Patent Document 2: Japanese Published Patent Application No.    2008-069221-   Patent Document 3: PCT International Publication No. 2008/035664

DISCLOSURE OF INVENTION

Phosphorescent materials emitting light of various colors have beendeveloped as reported in Patent Documents 1 to 3, development of novelmaterials emitting light of colors for intended purposes is anticipated.

In view of the above, one embodiment of the present invention provides,as a novel substance, an organometallic iridium complex that has highemission efficiency and a long lifetime and emits near-infrared light(emission wavelength: around 700 nm). Another embodiment of the presentinvention provides an organometallic iridium complex that has highquantum efficiency. Another embodiment of the present invention providesa light-emitting element, a light-emitting device, or a lighting devicethat has high emission efficiency.

One embodiment of the present invention is an organometallic iridiumcomplex having a ligand that is represented by General Formula (G0) andhas at least a dimethyl phenyl group and a quinoxaline skeleton. Thus,one embodiment of the present invention is an organometallic iridiumcomplex that has a structure represented by General Formula (G0).

In the formula, R¹ to R³ separately represent an alkyl group having 1 to6 carbon atoms, a phenyl group, or a phenyl group having an alkyl grouphaving 1 to 6 carbon atoms as a substituent.

Another embodiment of the present invention is an organometallic iridiumcomplex represented by General Formula (G1).

In the formula, R¹ to R³ separately represent an alkyl group having 1 to6 carbon atoms, a phenyl group, or a phenyl group having an alkyl grouphaving 1 to 6 carbon atoms as a substituent. In addition, L represents amonoanionic ligand.

In the general formula (G1), the monoanionic ligand is preferably any ofa monoanionic bidentate chelate ligand having a beta-diketone structure,a monoanionic bidentate chelate ligand having a carboxyl group, amonoanionic bidentate chelate ligand having a phenolic hydroxyl group,and a monoanionic bidentate chelate ligand in which two ligand elementsare both nitrogen. A monoanionic bidentate chelate ligand having abeta-diketone structure is particularly preferable.

The monoanionic ligand is preferably a ligand represented by any ofGeneral Formulae (L1) to (L7).

In the formulae, R⁷¹ to R¹¹¹ separately represent hydrogen, asubstituted or unsubstituted alkyl group having 1 to 6 carbon atoms, ahalogen group, a vinyl group, a substituted or unsubstituted haloalkylgroup having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxygroup having 1 to 6 carbon atoms, or a substituted or unsubstitutedalkylthio group having 1 to 6 carbon atoms. In addition, A¹ to A³separately represent nitrogen, sp² hybridized carbon bonded to hydrogen,and sp² hybridized carbon having a substituent. The substituentrepresents an alkyl group having 1 to 6 carbon atoms, a halogen group, ahaloalkyl group having 1 to 6 carbon atoms, and a phenyl group.

Another embodiment of the present invention is an organometallic iridiumcomplex represented by General Formula (G2).

In the formula, R¹ to R³ separately represent an alkyl group having 1 to6 carbon atoms, a phenyl group, or a phenyl group having an alkyl grouphaving 1 to 6 carbon atoms as a substituent. In addition, R⁴ and R⁵separately represent hydrogen, a substituted or unsubstituted alkylgroup having 1 to 6 carbon atoms, a halogen group, a vinyl group, asubstituted or unsubstituted haloalkyl group having 1 to 6 carbon atoms,a substituted or unsubstituted alkoxy group having 1 to 6 carbon atoms,and a substituted or unsubstituted alkylthio group having 1 to 6 carbonatoms.

Another embodiment of the present invention is an organometallic iridiumcomplex represented by Structural Formula (100).

Another embodiment of the present invention is an organometallic iridiumcomplex represented by Structural Formula (114).

The organometallic iridium complex of one embodiment of the presentinvention is very effective for increasing efficiency of alight-emitting element because the organometallic iridium complex canemit phosphorescence, that is, emission resulting from energy transferfrom a triplet excited state is possible. Thus, another embodiment ofthe present invention is a light-emitting element that includes theorganometallic iridium complex of one embodiment of the presentinvention.

In addition, the present invention includes, in its scope, not only alight-emitting device including the light-emitting element but also alighting device including the light-emitting device. The light-emittingdevice in this specification refers to an image display device and alight source (e.g., a lighting device). In addition, the light-emittingdevice includes, in its category, all of a module in which alight-emitting device is connected to a connector such as a flexibleprinted circuit (FPC), a tape carrier package (TCP), a module in which aprinted wiring board is provided on the tip of a TCP, and a module inwhich an integrated circuit (IC) is directly mounted on a light-emittingelement by a chip on glass (COG) method.

According to one embodiment of the present invention, an organometalliciridium complex that has high emission efficiency and a long lifetimeand emits near-infrared light (emission wavelength: around 700 nm) canbe provided as a novel substance. An organometallic iridium complex thathas high quantum efficiency can also be provided. Note that the use ofthe novel organometallic iridium complex enables a light-emittingelement, a light-emitting device, or a lighting device that has highemission efficiency to be provided. In addition, a light-emittingelement, a light-emitting device, or a lighting device that consumesless power can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a structure of a light-emitting element.

FIG. 2 illustrates a structure of a light-emitting element.

FIGS. 3A and 3B each illustrate a structure of a light-emitting element.

FIGS. 4A and 4B illustrate a light-emitting device.

FIG. 5 illustrates lighting devices.

FIG. 6 is a ¹H-NMR chart of an organometallic iridium complexrepresented by Structural Formula (100).

FIG. 7 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of the organometallic iridium complex represented by StructuralFormula (100).

FIG. 8 shows LC-MS measurement results of the organometallic iridiumcomplex represented by Structural Formula (100).

FIG. 9 is a ¹H-NMR chart of an organometallic iridium complexrepresented by Structural Formula (114).

FIG. 10 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of the organometallic iridium complex represented by StructuralFormula (114).

FIG. 11 shows LC-MS measurement results of the organometallic iridiumcomplex represented by Structural Formula (114).

FIG. 12 shows results of comparison between emission spectra oforganometallic iridium complexes.

FIG. 13 shows results of comparison between emission spectra oforganometallic iridium complexes.

FIG. 14 is a ¹H-NMR chart of an organometallic iridium complexrepresented by Structural Formula (118).

FIG. 15 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of the organometallic iridium complex represented by StructuralFormula (118).

FIG. 16 shows results of comparison between emission spectra oforganometallic iridium complexes.

FIG. 17 illustrates a light-emitting element.

FIG. 18 shows emission spectra of a light-emitting element 1, alight-emitting element 2, and a light-emitting element 3.

FIG. 19 shows results of comparison between emission spectra oforganometallic iridium complexes.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. Note that the present inventionis not limited to the following description, and various changes andmodifications can be made without departing from the spirit and scope ofthe present invention. Therefore, the present invention should not beconstrued as being limited to the description in the followingembodiments.

Embodiment 1

In this embodiment, an organometallic iridium complex of one embodimentof the present invention is described.

The organometallic iridium complex of one embodiment of the presentinvention is an organometallic iridium complex having a ligand that hasat least a dimethyl phenyl group and a quinoxaline skeleton. Note thatone embodiment of the organometallic iridium complex having the ligandthat has at least the dimethyl phenyl group and the quinoxalineskeleton, which is described in this embodiment, is an organometalliciridium complex having a structure represented by General Formula (G1).

In General Formula (G1), R¹ to R³ separately represent an alkyl grouphaving 1 to 6 carbon atoms, a phenyl group, or a phenyl group having analkyl group having 1 to 6 carbon atoms as a substituent. In addition, Lrepresents a monoanionic ligand.

In the general formula (G1), the monoanionic ligand is preferably any ofa monoanionic bidentate chelate ligand having a beta-diketone structure,a monoanionic bidentate chelate ligand having a carboxyl group, amonoanionic bidentate chelate ligand having a phenolic hydroxyl group,and a monoanionic bidentate chelate ligand in which two ligand elementsare both nitrogen. A monoanionic bidentate chelate ligand having abeta-diketone structure is particularly preferable.

The monoanionic ligand is preferably a ligand represented by any ofGeneral Formulae (L1) to (L7).

In the formulae, R⁷¹ to R¹¹¹ separately represent hydrogen, asubstituted or unsubstituted alkyl group having 1 to 6 carbon atoms, ahalogen group, a vinyl group, a substituted or unsubstituted haloalkylgroup having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxygroup having 1 to 6 carbon atoms, or a substituted or unsubstitutedalkylthio group having 1 to 6 carbon atoms. In addition, A¹ to A³separately represent nitrogen, sp² hybridized carbon bonded to hydrogen,and sp² hybridized carbon having a substituent. The substituentrepresents an alkyl group having 1 to 6 carbon atoms, a halogen group, ahaloalkyl group having 1 to 6 carbon atoms, and a phenyl group.

Note that specific examples of the substituted or unsubstituted alkylgroup having 1 to 6 carbon atoms in R¹ to R³ include a methyl group, anethyl group, a propyl group, an isopropyl group, a butyl group, asec-butyl group, an isobutyl group, a tert-butyl group, a pentyl group,an isopentyl group, a sec-pentyl group, a tert-pentyl group, a neopentylgroup, a hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexylgroup, a neohexyl group, a 3-methylpentyl group, a 2-methylpentyl group,a 2-ethylbutyl group, a 1,2-dimethylbutyl group, and a 2,3-dimethylbutylgroup.

Note that the organometallic iridium complex of one embodiment of thepresent invention has a structure in which a phenyl group that is bondedto a quinoxaline skeleton and bonded to iridium has two substituentsthat are any of an alkyl group having 1 to 6 carbon atoms, a phenylgroup, and a phenyl group having an alkyl group having 1 to 6 carbonatoms as a substituent, and the two substituents are bonded to the4-position and the 6-position of a 2-(2-quinoxalinyl)phenyl group bondedto iridium. This structure enables the emission wavelength (peakwavelength) of the organometallic iridium complex of one embodiment ofthe present invention to be longer than the emission wavelength of anorganometallic iridium complex that does not have such substituents. Inother words, the organometallic iridium complex of one embodiment of thepresent invention is a novel substance that emits near-infrared lightand has high quantum efficiency.

Another embodiment of the present invention is an organometallic iridiumcomplex represented by General Formula (G2).

In General Formula (G2), R′ to R³ separately represent an alkyl grouphaving 1 to 6 carbon atoms, a phenyl group, or a phenyl group having analkyl group having 1 to 6 carbon atoms as a substituent. In addition, R⁴and R⁵ separately represent hydrogen, a substituted or unsubstitutedalkyl group having 1 to 6 carbon atoms, a halogen group, a vinyl group,a substituted or unsubstituted haloalkyl group having 1 to 6 carbonatoms, a substituted or unsubstituted alkoxy group having 1 to 6 carbonatoms, and a substituted or unsubstituted alkylthio group having 1 to 6carbon atoms.

Next, specific structural formulae of the above-described organometalliciridium complexes of embodiments of the present invention are shown(Structural Formulae (100) to (120)). Note that the present invention isnot limited thereto.

Note that organometallic iridium complexes represented by StructuralFormulae (100) to (120) are novel substances that are capable ofemitting phosphorescence. Note that there can be geometrical isomers andstereoisomers of these substances depending on the type of the ligand.The organometallic iridium complex of one embodiment of the presentinvention includes all of these isomers.

Next, an example of a method of synthesizing the organometallic iridiumcomplex represented by General Formula (G1) is described.

<<Method of Synthesizing Quinoxaline Derivative Represented by GeneralFormula (G0)>>

An example of a method of synthesizing the quinoxaline derivativerepresented by General Formula (G0) is described.

Note that in General Formula (G0), R¹ to R³ separately represent analkyl group having 1 to 6 carbon atoms, a phenyl group, or a phenylgroup having an alkyl group having 1 to 6 carbon atoms as a substituent.

Three Synthesis Schemes (A1), (A2), and (A3) of the quinoxalinederivative represented by General Formula (G0) are shown below.

In Synthesis Scheme (A1), 3,5-dialkylphenyl boronic acid (a1) is coupledwith a halogenated quinoxaline compound (a1′) to obtain the quinoxalinederivative (G0).

In Synthesis Scheme (A2), α-diketone (a2) is reacted witho-phenylenediamine (a2′) to obtain the quinoxaline derivative (G0).

In Synthesis Scheme (A3), in the case where R¹ and R² are the same alkylgroup, alkyl boronic acid (a3) is coupled with a quinoxaline compoundsubstituted with 3,5-dihalogenated phenyl (a3′) to obtain thequinoxaline derivative (G0); meanwhile, in the case where R¹ and R² aredifferent alkyl groups, a quinoxaline compound substituted withhalogenated phenyl (a3″) that is an intermediate of the quinoxalinecompound substituted with halogenated phenyl is obtained first, and thenthe intermediate is coupled with alkyl boronic acid (a3′″), so that thequinoxaline derivative (G0) is obtained. Note that, in the formula, Xrepresents a halogen element.

Other than the above-described three methods, there are a plurality ofknown methods of synthesizing the derivative (G0). Thus, any of themethods can be employed.

Since many kinds of the compounds (a1), (a1′), (a2), (a2′), (a3), (a3′),(a3″), and (a3′″) in the schemes are commercially available or can besynthesized, many kinds of quinoxaline derivatives represented byGeneral Formula (G0) can be synthesized. Thus, a feature of theorganometallic iridium complex of one embodiment of the presentinvention is the abundance of ligand variations.

<<Method of Synthesizing Organometallic Iridium Complex of OneEmbodiment of the Present Invention Represented by General Formula(G1)>>

Next, a method of synthesizing the organometallic iridium complex of oneembodiment of the present invention represented by General Formula (G1),which is formed using the quinoxaline derivative represented by GeneralFormula (G0), is described.

In General Formula (G1), R¹ to R³ separately represent an alkyl grouphaving 1 to 6 carbon atoms, a phenyl group, or a phenyl group having analkyl group having 1 to 6 carbon atoms as a substituent. In addition, Lrepresents a monoanionic ligand.

Synthesis Scheme (B) of the organometallic iridium complex representedby General Formula (G1) is shown below.

In Synthesis Scheme (B), R¹ to R³ separately represent an alkyl grouphaving 1 to 6 carbon atoms, a phenyl group, or a phenyl group having analkyl group having 1 to 6 carbon atoms as a substituent. In addition, Yrepresents a halogen.

As shown in Synthesis Scheme (B), the quinoxaline derivative representedby General Formula (G0) and an iridium compound containing a halogen(e.g., iridium chloride, iridium bromide, or iridium iodide) are heatedin an inert gas atmosphere using no solvent, an alcohol-based solvent(e.g., glycerol, ethylene glycol, 2-methoxyethanol, or 2-ethoxyethanol)alone, or a mixed solvent of water and one or more of the alcohol-basedsolvents, whereby a dinuclear complex (P), which is one type of anorganometallic iridium complex having a halogen-bridged structure, canbe obtained.

There is no particular limitation on a heating means, and an oil bath, asand bath, or an aluminum block may be used. Alternatively, microwavescan be used as a heating means.

Furthermore, as shown in Synthesis Scheme (C), the dinuclear complex (P)obtained in Synthesis Scheme (B) is reacted with a ligand HL in an inertgas atmosphere, whereby a proton of the ligand HL is eliminated and amonoanionic ligand L coordinates to iridium that is a central metal.Thus, the organometallic iridium complex of one embodiment of thepresent invention represented by General Formula (G1) can be obtained.

In Synthesis Scheme (C), R¹ to R³ separately represent an alkyl grouphaving 1 to 6 carbon atoms, a phenyl group, or a phenyl group having analkyl group having 1 to 6 carbon atoms as a substituent. In addition, Lrepresents a monoanionic ligand.

There is no particular limitation on a heating means, and an oil bath, asand bath, or an aluminum block may be used. Alternatively, microwavescan be used as a heating means.

The example of a method of synthesizing the organometallic iridiumcomplex of one embodiment of the present invention is described above;however, one embodiment of the present invention is not limited to theexamples, and any other synthesis methods may be employed.

The above-described organometallic iridium complex of one embodiment ofthe present invention can emit phosphorescence and thus can be used as alight-emitting material or a light-emitting substance of alight-emitting element.

With the use of the organometallic iridium complex of one embodiment ofthe present invention, a light-emitting element, a light-emittingdevice, or a lighting device with high emission efficiency can beobtained. It is also possible to obtain a light-emitting element, alight-emitting device, or a lighting device with low power consumption.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 2

In this embodiment, a light-emitting element in which the organometalliciridium complex described in Embodiment 1 as one embodiment of thepresent invention is used for a light-emitting layer is described withreference to FIG. 1.

In a light-emitting element described in this embodiment, as illustratedin FIG. 1, an EL layer 102 including a light-emitting layer 113 isinterposed between a pair of electrodes (a first electrode (anode) 101and a second electrode (cathode) 103), and the EL layer 102 includes ahole-injection layer 111, a hole-transport layer 112, anelectron-transport layer 114, an electron-injection layer 115, acharge-generation layer (E) 116, and the like in addition to thelight-emitting layer 113.

By application of voltage to such a light-emitting element, holesinjected from the first electrode 101 side and electrons injected fromthe second electrode 103 side recombine in the light-emitting layer 113to raise the organometallic iridium complex to an excited state. Then,light is emitted when the organometallic iridium complex in the excitedstate relaxes to the ground state. Thus, the organometallic iridiumcomplex in one embodiment of the present invention functions as alight-emitting substance in the light-emitting element.

The hole-injection layer 111 included in the EL layer 102 contains asubstance having a high hole-transport property and an acceptorsubstance. When electrons are extracted from the substance having a highhole-transport property owing to the acceptor substance, holes aregenerated. Thus, holes are injected from the hole-injection layer 111into the light-emitting layer 113 through the hole-transport layer 112.

The charge-generation layer (E) 116 contains a substance having a highhole-transport property and an acceptor substance. Electrons areextracted from the substance having a high hole-transport property owingto the acceptor substance, and the extracted electrons are injected fromthe electron-injection layer 115 having an electron-injection propertyinto the light-emitting layer 113 through the electron-transport layer114.

A specific example in which the light-emitting element described in thisembodiment is fabricated is described.

As the first electrode (anode) 101 and the second electrode (cathode)103, a metal, an alloy, an electrically conductive compound, a mixturethereof, and the like can be used. Specifically, indium oxide-tin oxide(indium tin oxide), indium oxide-tin oxide containing silicon or siliconoxide, indium oxide-zinc oxide (indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide, gold (Au), platinum (Pt),nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe),cobalt (Co), copper (Cu), palladium (Pd), and titanium (Ti) can be used.In addition, an element belonging to Group 1 or Group 2 of the periodictable, for example, an alkali metal such as lithium (Li) or cesium (Cs),an alkaline earth metal such as calcium (Ca) or strontium (Sr),magnesium (Mg), an alloy containing such an element (MgAg, AlLi), a rareearth metal such as europium (Eu) or ytterbium (Yb), an alloy containingsuch an element, graphene, and the like can be used. The first electrode(anode) 101 and the second electrode (cathode) 103 can be formed by, forexample, a sputtering method, an evaporation method (e.g., a vacuumevaporation method), or the like.

Examples of the substance having a high hole-transport property used forthe hole-injection layer 111, the hole-transport layer 112, and thecharge-generation layer (E) 116 include aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB ora-NPD), NN-bis(3-methylphenyl)-N,N-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB);3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2); and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1). Other examples include4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-Carbazole (abbreviation: CzPA).The substances given here are mainly ones that have a hole mobility of10⁻⁶ cm²/Vs or higher. Note that any substance other than the substancesgiven above may also be used as long as the hole-transport property ishigher than the electron-transport property.

Other examples include a high molecular compound such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine)(abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD).

Examples of the acceptor substance that is used for the hole-injectionlayer 111 and the charge-generation layer (E) 116 include oxides ofmetals belonging to any of Group 4 to Group 8 of the periodic table.Specifically, molybdenum oxide is particularly preferable.

The light-emitting layer 113 contains any of the organometallic iridiumcomplexes described in Embodiment 1 as a guest material serving as alight-emitting substance and a substance that has higher tripletexcitation energy than this organometallic iridium complex as a hostmaterial.

Preferable examples of the substance (i.e., host material) used fordispersing any of the above-described organometallic iridium complexesinclude compounds having an arylamine skeleton, such as2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviation: TPAQn) and NPB;carbazole derivatives such as CBP and4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA); andmetal complexes such as bis[2-(2-hydroxyphenyl)pyridinato]zinc(abbreviation: Znpp₂), bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: Zn(BOX)₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), and tris(8-quinolinolato)aluminum (abbreviation: Alq₃).Alternatively, a high molecular compound such as PVK can be used.

Note that in the case where the light-emitting layer 113 contains theabove-described organometallic iridium complex (guest material) and thehost material, phosphorescence with high emission efficiency can beobtained from the light-emitting layer 113.

The electron-transport layer 114 is a layer containing a substancehaving a high electron-transport property. For the electron-transportlayer 114, a metal complex such as Alq₃,tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),BAlq, Zn(BOX)₂, or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc(II)(abbreviation: Zn(BTZ)₂) can be used. A heteroaromatic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen),bathocuproine (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can alsobe used. A high molecular compound such as poly(2,5-pyridinediyl)(abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py) orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can also be used. The substances given here aremainly ones that have an electron mobility of 10⁻⁶ cm²/Vs or higher.Note that any substance other than the substances given above may beused for the electron-transport layer 114 as long as theelectron-transport property is higher than the hole-transport property.

The electron-transport layer 114 is not limited to a single layer, andmay be a stack of two or more layers containing any of the substancesgiven above.

The electron-injection layer 115 contains a substance having a highelectron-injection property. For the electron-injection layer 115, analkali metal, an alkaline earth metal, or a compound thereof, such aslithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF₂),or lithium oxide (LiO_(x)) can be used. A rare earth metal compound likeerbium fluoride (ErF₃) can also be used. Any of the above substances forforming the electron-transport layer 114 can also be used.

A composite material in which an organic compound and an electron donor(donor) are mixed may also be used for the electron-injection layer 115.Such a composite material is excellent in an electron-injection propertyand an electron-transport property because electrons are generated inthe organic compound by the electron donor. In this case, the organiccompound is preferably a material that is excellent in transporting thegenerated electrons. Specifically, for example, the substances forforming the electron-transport layer 114 (e.g., a metal complex or aheteroaromatic compound), which are given above, can be used. As theelectron donor, a substance showing an electron-donating property withrespect to the organic compound may be used. Specifically, an alkalimetal, an alkaline earth metal, and a rare earth metal are preferable,and lithium, cesium, magnesium, calcium, erbium, ytterbium, and the likeare given. In addition, an alkali metal oxide or an alkaline earth metaloxide is preferable, and lithium oxide, calcium oxide, and barium oxideare given. Lewis base such as magnesium oxide can also be used. Anorganic compound such as tetrathiafulvalene (abbreviation: TTF) can alsobe used.

Note that each of the above-described hole-injection layer 111,hole-transport layer 112, light-emitting layer 113, electron-transportlayer 114, electron-injection layer 115, and charge-generation layer (E)116 can be formed by a method such as an evaporation method (e.g., avacuum evaporation method), an ink-jet method, or a coating method.

In the above-described light-emitting element, current flows because ofa potential difference applied between the first electrode 101 and thesecond electrode 103 and holes and electrons are recombined in the ELlayer 102, whereby light is emitted. Then, the emitted light isextracted outside through one or both of the first electrode 101 and thesecond electrode 103. Thus, one or both of the first electrode 101 andthe second electrode 103 are electrodes having light-transmittingproperties.

The above-described light-emitting element can emit phosphorescenceoriginating from the organometallic iridium complex and thus can havehigher efficiency than a light-emitting element using a fluorescentcompound.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 3

In this embodiment, as one embodiment of the present invention, alight-emitting element in which two or more kinds of organic compoundsas well as an organometallic iridium complex are used for alight-emitting layer is described.

A light-emitting element described in this embodiment includes an ELlayer 203 between a pair of electrodes (an anode 201 and a cathode 202)as illustrated in FIG. 2. Note that the EL layer 203 includes at least alight-emitting layer 204 and may include a hole-injection layer, ahole-transport layer, an electron-transport layer, an electron-injectionlayer, a charge-generation layer (E), and the like. Note that for thehole-injection layer, the hole-transport layer, the electron-transportlayer, the electron-injection layer, and the charge-generation layer(E), the substances given in Embodiment 2 can be used.

The light-emitting layer 204 described in this embodiment contains aphosphorescent compound 205 using the organometallic iridium complexdescribed in Embodiment 1, a first organic compound 206, and a secondorganic compound 207. Note that the phosphorescent compound 205 is aguest material in the light-emitting layer 204. One of the first organiccompound 206 and the second organic compound 207, the content of whichis higher than that of the other in the light-emitting layer 204, is ahost material in the light-emitting layer 204.

When the light-emitting layer 204 has the structure in which the guestmaterial is dispersed in the host material, crystallization of thelight-emitting layer can be suppressed. In addition, it is possible tosuppress concentration quenching due to high concentration of the guestmaterial, and thus the light-emitting element can have higher emissionefficiency.

Note that it is preferable that the triplet excitation energy level (T₁level) of each of the first organic compound 206 and the second organiccompound 207 be higher than that of the phosphorescent compound 205.This is because, when the T₁ level of the first organic compound 206 (orthe second organic compound 207) is lower than that of thephosphorescent compound 205, the triplet excitation energy of thephosphorescent compound 205, which is to contribute to light emission,is quenched by the first organic compound 206 (or the second organiccompound 207) and accordingly the emission efficiency is decreased.

Here, for improvement in efficiency of energy transfer from a hostmaterial to a guest material, Förster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), whichare known as mechanisms of energy transfer between molecules, areconsidered. According to the mechanisms, it is preferable that anemission spectrum of a host material (fluorescence spectrum in energytransfer from a singlet excited state, phosphorescence spectrum inenergy transfer from a triplet excited state) largely overlap with anabsorption spectrum of a guest material (specifically, spectrum in anabsorption band on the longest wavelength (lowest energy) side).However, in general, it is difficult to obtain an overlap between afluorescence spectrum of a host material and an absorption spectrum inan absorption band on the longest wavelength (lowest energy) side of aguest material. The reason for this is as follows: if the fluorescencespectrum of the host material overlaps with the absorption spectrum inthe absorption band on the longest wavelength (lowest energy) side ofthe guest material, since a phosphorescence spectrum of the hostmaterial is located on a longer wavelength (lower energy) side ascompared to the fluorescence spectrum, the T₁ level of the host materialbecomes lower than the T₁ level of the phosphorescent compound and theabove-described problem of quenching occurs; yet, when the host materialis designed in such a manner that the T₁ level of the host material ishigher than the T₁ level of the phosphorescent compound to avoid theproblem of quenching, the fluorescence spectrum of the host material isshifted to the shorter wavelength (higher energy) side; thus, thefluorescence spectrum does not have any overlap with the absorptionspectrum in the absorption band on the longest wavelength (lowestenergy) side of the guest material. For that reason, in general, it isdifficult to obtain an overlap between a fluorescence spectrum of a hostmaterial and an absorption spectrum in an absorption band on the longestwavelength (lowest energy) side of a guest material so as to maximizeenergy transfer from a singlet excited state of the host material.

Thus, in this embodiment, a combination of the first organic compound206 and the second organic compound 207 preferably forms an exciplex(also referred to as excited complex). In this case, the first organiccompound 206 and the second organic compound 207 form an exciplex at thetime of recombination of carriers (electrons and holes) in thelight-emitting layer 204. Thus, in the light-emitting layer 204, afluorescence spectrum of the first organic compound 206 and that of thesecond organic compound 207 are converted into an emission spectrum ofthe exciplex that is located on the longer wavelength side. Moreover,when the first organic compound 206 and the second organic compound 207are selected in such a manner that the emission spectrum of the exciplexlargely overlaps with the absorption spectrum of the guest material,energy transfer from a singlet excited state can be maximized. Note thatalso in the case of a triplet excited state, energy transfer from theexciplex, not the host material, is assumed to occur.

For the phosphorescent compound 205, the organometallic iridium complexdescribed in Embodiment 1 is used. Although the combination of the firstorganic compound 206 and the second organic compound 207 can bedetermined such that an exciplex is formed, a combination of a compoundwhich is likely to accept electrons (a compound having anelectron-trapping property) and a compound which is likely to acceptholes (a compound having a hole-trapping property) is preferablyemployed.

Examples of the compound that easily accepts electrons include2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), and6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:6mDBTPDBq-II).

Examples of the compound that easily accepts holes include4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9′-bifluorene(abbreviation: DPA2SF),N,N-bis(9-phenylcarbazol-3-yl)-N,N-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N-(9,9-dimethyl-2-N,N′-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),N,N′,N″-triphenyl-N,N′,N″-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B), 2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene (abbreviation: PCASF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),N,N-bis[4-(carbazol-9-yl)phenyl]-N,N-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N-phenyl-N-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2), and3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2).

The above-described first and second organic compounds 206 and 207 arenot limited to the above examples. The combination is determined so thatan exciplex can be formed, the emission spectrum of the exciplexoverlaps with the absorption spectrum of the phosphorescent compound205, and the peak of the emission spectrum of the exciplex has a longerwavelength than the peak of the absorption spectrum of thephosphorescent compound 205.

Note that in the case where a compound which is likely to acceptelectrons and a compound which is likely to accept holes are used forthe first organic compound 206 and the second organic compound 207,carrier balance can be controlled by the mixture ratio of the compounds.Specifically, the ratio of the first organic compound to the secondorganic compound is preferably 1:9 to 9:1.

In the light-emitting element described in this embodiment, energytransfer efficiency can be improved owing to energy transfer utilizingan overlap between an emission spectrum of an exciplex and an absorptionspectrum of a phosphorescent compound. Thus, high external quantumefficiency of the light-emitting element can be achieved.

Note that in another structure of one embodiment of the presentinvention, the light-emitting layer 204 can be formed using a hostmolecule having a hole-trapping property and a host molecule having anelectron-trapping property as the two kinds of organic compounds (thefirst organic compound 206 and the second organic compound 207) otherthan the phosphorescent compound 205 (guest material) so that aphenomenon (guest coupled with complementary hosts: GCCH) occurs inwhich holes and electrons are introduced to guest molecules existing inthe two kinds of host molecules and the guest molecules are brought intoan excited state.

At this time, the host molecule having a hole-trapping property and thehost molecule having an electron-trapping property can be respectivelyselected from the above compounds that easily accept holes and the abovecompounds that easily accept electrons.

The structure of the light-emitting element described in this embodimentis an example. The light-emitting element of one embodiment of thepresent invention can have a microcavity structure in addition to thestructure.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 4

In this embodiment, as one embodiment of the present invention, alight-emitting element (hereinafter referred to as tandem light-emittingelement) in which a charge-generation layer is provided between aplurality of EL layers is described.

A light-emitting element described in this embodiment is a tandemlight-emitting element including a plurality of EL layers (a first ELlayer 302(1) and a second EL layer 302(2)) between a pair of electrodes(a first electrode 301 and a second electrode 304) as illustrated inFIG. 3A.

In this embodiment, the first electrode 301 functions as an anode, andthe second electrode 304 functions as a cathode. Note that the firstelectrode 301 and the second electrode 304 can have structures similarto those described in Embodiment 2. In addition, although the pluralityof EL layers (the first EL layer 302(1) and the second EL layer 302(2))may have a structure similar to that of the EL layer described inEmbodiment 2 or 3, any of the EL layers may have a structure similar tothat of the EL layer described in Embodiment 2 or 3. In other words, thestructures of the first EL layer 302(1) and the second EL layer 302(2)may be the same or different from each other and can be similar to thoseof the EL layers described in Embodiment 2 or 3.

In addition, a charge-generation layer (I) 305 is provided between theplurality of EL layers (the first EL layer 302(1) and the second ELlayer 302(2)). The charge-generation layer (I) 305 has a function ofinjecting electrons into one of the EL layers and injecting holes intothe other of the EL layers when voltage is applied between the firstelectrode 301 and the second electrode 304. In this embodiment, whenvoltage is applied such that the potential of the first electrode 301 ishigher than that of the second electrode 304, the charge-generationlayer (I) 305 injects electrons into the first EL layer 302(1) andinjects holes into the second EL layer 302(2).

Note that in terms of light extraction efficiency, the charge-generationlayer (I) 305 preferably has a light-transmitting property with respectto visible light (specifically, the charge-generation layer (I) 305 hasa visible light transmittance of 40% or more). The charge-generationlayer (I) 305 functions even if it has lower conductivity than the firstelectrode 301 or the second electrode 304.

The charge-generation layer (I) 305 may have either a structure in whichan electron acceptor (acceptor) is added to an organic compound having ahigh hole-transport property or a structure in which an electron donor(donor) is added to an organic compound having a high electron-transportproperty. Alternatively, both of these structures may be stacked.

In the case of the structure in which an electron acceptor is added toan organic compound having a high hole-transport property, the organiccompound having a high hole-transport property can be, for example, anaromatic amine compound such as NPB, TPD, TDATA, MTDATA, or BSPB, or thelike. The substances given here are mainly ones that have a holemobility of 10⁻⁶ cm²/Vs or higher. Note that any substance other thanthe substances given above may be used as long as the hole-transportproperty is higher than the electron-transport property.

As the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. Specifically, it ispreferable to use vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, andrhenium oxide because of their high electron accepting properties. Amongthese, molybdenum oxide is especially preferable because it is stable inthe air, has a low hygroscopic property, and is easy to handle.

In the case of the structure in which an electron donor is added to anorganic compound having a high electron-transport property, as theorganic compound having a high electron-transport property, for example,a metal complex having a quinoline skeleton or a benzoquinolineskeleton, such as Alq, Almq₃, BeBq₂, or BAlq, or the like can be used. Ametal complex having an oxazole-based ligand or a thiazole-based ligand,such as Zn(BOX)₂ or Zn(BTZ)₂ can also be used. It is also possible touse PBD, OXD-7, TAZ, Bphen, BCP, or the like instead of such a metalcomplex. The substances given here are mainly ones that have an electronmobility of 10⁻⁶ cm²/Vs or higher. Note that any substance other thanthe substances given above may be used as long as the electron-transportproperty is higher than the hole-transport property.

As the electron donor, it is possible to use an alkali metal, analkaline earth metal, a rare earth metal, a metal belonging to Group 2to Group 13 of the periodic table, or an oxide or carbonate thereof.Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca),ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or thelike is preferably used. An organic compound such astetrathianaphthacene may also be used as the electron donor.

Note that forming the charge-generation layer (I) 305 by using any ofthe above materials can suppress an increase in drive voltage caused bythe stack of the EL layers.

Although the light-emitting element including two EL layers is describedin this embodiment, the present invention can be similarly applied to alight-emitting element in which n EL layers (302(1) to 302(n)) (n isthree or more) are stacked as illustrated in FIG. 3B. In the case wherea plurality of EL layers are included between a pair of electrodes as inthe light-emitting element according to this embodiment, by providingcharge-generation layers (I) (305(1) to 305(n−1)) between the EL layers,light emission in a high luminance region can be obtained with currentdensity kept low. Since the current density can be kept low, the elementcan have a long lifetime. When the light-emitting element is used forlight-emitting devices, and lighting devices each having a largelight-emitting area, voltage drop due to resistance of an electrodematerial can be reduced, thereby achieving uniform light emission in alarge area.

When the EL layers have different emission colors, a desired emissioncolor can be obtained from the whole light-emitting element. Forexample, in the light-emitting element having two EL layers, when anemission color of the first EL layer and an emission color of the secondEL layer are made to be complementary colors, a light-emitting elementemitting white light as a whole light-emitting element can also beobtained. Note that “complementary colors” refer to colors that canproduce an achromatic color when combined. In other words, combinationof complementary colors allows white light emission to be obtained.

The same can be applied to a light-emitting element having three ELlayers. For example, the light-emitting element as a whole can providewhite light emission when the emission color of the first EL layer isred, the emission color of the second EL layer is green, and theemission color of the third EL layer is blue.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 5

In this embodiment, a light-emitting device that includes alight-emitting element in which the organometallic iridium complex ofone embodiment of the present invention is used in a light-emittinglayer is described.

The light-emitting device may be either a passive matrix light-emittingdevice or an active matrix light-emitting device. Note that any of thelight-emitting elements described in the other embodiments can beapplied to the light-emitting device described in this embodiment.

In this embodiment, an active matrix light-emitting device is describedwith reference to FIGS. 4A and 4B.

FIG. 4A is a top view illustrating a light-emitting device and FIG. 4Bis a cross-sectional view taken along the chain line A-A′ in FIG. 4A.The active matrix light-emitting device of this embodiment includes apixel portion 402 provided over an element substrate 401, a drivercircuit portion (a source line driver circuit) 403, and driver circuitportions (gate line driver circuits) 404 a and 404 b. The pixel portion402, the driver circuit portion 403, and the driver circuit portions 404a and 404 b are sealed with a sealant 405 between the element substrate401 and a sealing substrate 406.

In addition, over the element substrate 401, a lead wiring 407 forconnecting an external input terminal, through which a signal (e.g., avideo signal, a clock signal, a start signal, or a reset signal) or anelectric potential is transmitted to the driver circuit portion 403 andthe driver circuit portions 404 a and 404 b, is provided. Here, anexample is described in which a flexible printed circuit (FPC) 408 isprovided as the external input terminal. Although only the FPC is shownhere, the FPC may be provided with a printed wiring board (PWB). Thelight-emitting device in the present specification includes, in itscategory, not only the light-emitting device itself but also thelight-emitting device provided with the FPC or the PWB.

Next, a cross-sectional structure is described with reference to FIG.4B. The driver circuit portion and the pixel portion are formed over theelement substrate 401; here are illustrated the driver circuit portion403 that is the source line driver circuit and the pixel portion 402.

The driver circuit portion 403 is an example where a CMOS circuit isformed, which is a combination of an n-channel FET 409 and a p-channelFET 410. Note that a circuit included in the driver circuit portion maybe formed using various CMOS circuits, PMOS circuits, or NMOS circuits.Any of a staggered type FET and a reverse-staggered type FET may beused. Furthermore, the crystallinity of a semiconductor film used in theFET is not limited and may be amorphous or crystalline. Examples of asemiconductor material include Group IV semiconductors (e.g., siliconand gallium), compound semiconductors (including oxide semiconductors),and organic semiconductors. Although a driver integrated type in whichthe driver circuit is formed over the substrate is described in thisembodiment, the driver circuit is not necessarily be formed over thesubstrate, and the driver circuit can be formed outside, not over thesubstrate.

The pixel portion 402 is formed of a plurality of pixels each of whichincludes a switching FET 411, a current control FET 412, and a firstelectrode (anode) 413 electrically connected to a wiring (a sourceelectrode or a drain electrode) of the current control FET 412. Aninsulator 414 is formed to cover an end portion of the first electrode(anode) 413.

The insulator 414 preferably has a curved surface with curvature at anupper end portion or a lower end portion thereof in order to obtainfavorable coverage by a film that is to be stacked over the insulator414. For example, the insulator 414 can be formed using either anegative photosensitive resin or a positive photosensitive resin. Thematerial of the insulator 414 is not limited to an organic compound andan inorganic compound such as silicon oxide or silicon oxynitride canalso be used.

An EL layer 415 and a second electrode (cathode) 416 are stacked overthe first electrode (anode) 413. The EL layer 415 is provided with atleast a light-emitting layer in which the organometallic iridium complexof one embodiment of the present invention can be used. In addition tothe light-emitting layer, a hole-injection layer, a hole-transportlayer, an electron-transport layer, an electron-injection layer, acharge-generation layer, and the like can be provided as appropriate inthe EL layer 415.

A light-emitting element 417 is formed of a stacked structure of thefirst electrode (anode) 413, the EL layer 415, and the second electrode(cathode) 416. For the first electrode (anode) 413, the EL layer 415,and the second electrode (cathode) 416, the materials described inEmbodiment 2 can be used. Although not illustrated, the second electrode(cathode) 416 is electrically connected to the FPC 408 that is anexternal input terminal.

Although the cross-sectional view of FIG. 4B illustrates only onelight-emitting element 417, a plurality of light-emitting elements arearranged in matrix in the pixel portion 402. Light-emitting elementsthat emit light of three kinds of colors (R, G, and B) are selectivelyformed in the pixel portion 402, whereby a light-emitting device capableof full color display can be obtained. Alternatively, a light-emittingdevice capable of full color display may be fabricated by a combinationwith color filters.

In addition, the sealing substrate 406 is attached to the elementsubstrate 401 with the sealant 405, so that a light-emitting element 417is provided in a space 418 surrounded by the element substrate 401, thesealing substrate 406, and the sealant 405. Note that the space 418 maybe filled with an inert gas (e.g., nitrogen or argon) or the sealant405.

Note that an epoxy-based resin or glass frit is preferably used as thesealant 405. It is preferable that such a material do not transmitmoisture or oxygen as much as possible. As the sealing substrate 406, aglass substrate, a quartz substrate, or a plastic substrate formed offiber-reinforced plastic (FRP), poly(vinyl fluoride) (PVF), a polyester,an acrylic resin, or the like can be used. In the case where glass fritis used as the sealant, the element substrate 401 and the sealingsubstrate 406 are preferably glass substrates in terms of adhesion.

As described above, an active matrix light-emitting device can beobtained.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 6

In this embodiment, examples of a lighting device in which alight-emitting device including the organometallic iridium complex ofone embodiment of the present invention is used are described withreference to FIG. 5.

FIG. 5 illustrates an example in which the light-emitting device is usedas an indoor lighting device 8001. Since the light-emitting device canhave a large area, it can be used for a lighting device having a largearea. In addition, a lighting device 8002 in which a light-emittingregion has a curved surface can also be obtained with the use of ahousing with a curved surface. A light-emitting element included in thelight-emitting device described in this embodiment is in a thin filmform, which allows the housing to be designed more freely. Therefore,the lighting device can be elaborately designed in a variety of ways. Awall of the room may be provided with a large-sized lighting device8003.

In addition, when the light-emitting device is used for a table by beingused as a surface of a table, a lighting device 8004 which has afunction as a table can be obtained. When the light-emitting device isused as part of other furniture, a lighting device which has a functionas the furniture can be obtained.

As described above, a variety of lighting devices in which thelight-emitting device is used can be obtained. Note that these lightingdevices are also embodiments of the present invention.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Example 1 Synthesis Example 1

In this example, a method of synthesizing bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-2-quinoxalinyl-κN]phenyl-κC}(2,2′,6,6′-tetramethyl-3,5-heptanedionato-κ²O,O′)iridium(III) (abbreviation: [Ir(dmdpq)₂(dpm)]) that is an organometalliciridium complex of one embodiment of the present invention and isrepresented by Structural Formula (100) in Embodiment 1 is described. Astructure of [Ir(dmdpq)₂(dpm)] is shown below.

Step 1: Synthesis of 2,3-bis(3,5-dimethylphenyl)quinoxaline(Abbreviation: Hdmdpq)

First, 1.2 g of o-phenylenediamine, 3.0 g of3,3′,5,5′-tetramethylbenzyl, and 30 mL of ethanol were put in a 200-mLthree-neck flask, and the air in the flask was replaced with nitrogen.After that, the mixture was heated at 90° C. for 7.5 hours to cause areaction. Water was added to the reacted solution, and the organic layerwas extracted with dichloromethane. The obtained organic layer waswashed with water and saturated saline, and was dried with magnesiumsulfate. The solution obtained by the drying was filtered. The solventin this solution was distilled off, and the obtained residue wasdissolved in toluene and filtered through a filter aid in which Celite,alumina, and Celite were stacked in this order to give a quinoxalinederivative Hdmdpq that was a target substance as white powder in a yieldof 87%. Synthesis Scheme (a-1) of Step 1 is shown below.

Step 2: Synthesis of di-μ-chloro-tetrakis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-2-quinoxalinyl-κN]phenyl-κC}diiridium(III)(Abbreviation: [Ir(dmdpq)₂Cl]₂)>

Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.08 g of Hdmdpq obtainedin Step 1, and 0.48 g of iridium chloride hydrate (IrCl₃.H₂O) (producedby Sigma-Aldrich Corporation) were put in a recovery flask equipped witha reflux pipe, and the air in the flask was replaced with argon. Afterthat, irradiation with microwaves (2.45 GHz, 100 W) was performed for 1hour to cause a reaction. The solvent was distilled off, and then theobtained residue was suction-filtered and washed with ethanol to give adinuclear complex [Ir(dmdpq)₂Cl]₂ as brown powder in a yield of 68%.Synthesis Scheme (a-2) of Step 2 is shown below.

Step 3: Synthesis of bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-2-quinoxalinyl-κN]phenyl-κC}(2,2′,6,6′-tetramethyl-3,5-heptanedionato-κ²O,O′)iridium(III) (Abbreviation: [Ir(dmdpq)₂(dpm)])>

Furthermore, 30 mL of 2-ethoxyethanol, 0.98 g of [Ir(dmdpq)₂Cl]₂ thatwas the dinuclear complex obtained in Step 2, 0.16 g ofdipivaloylmethane (abbreviation: Hdpm), and 0.57 g of sodium carbonatewere put in a recovery flask equipped with a reflux pipe, and the air inthe flask was replaced with argon. After that, the mixture was heated byirradiation with microwaves (2.45 GHz, 120 W) for 60 minutes. Here, 0.16g of Hdpm was further added, and heating was performed by irradiationwith microwaves (2.45 GHz, 120 W) for 60 minutes. Water was added to thereacted solution, and the organic layer was extracted withdichloromethane. The obtained organic layer was washed with water andsaturated saline, and was dried with magnesium sulfate. The solutionobtained by the drying was filtered. This solution was distilled off,and then the obtained residue was purified by flash columnchromatography using dichloromethane as a developing solvent to give[Ir(dmdpq)₂(dpm)], which is the organometallic iridium complex of oneembodiment of the present invention, as brown powder in a yield of 6%.Synthesis Scheme (a-3) of Step 3 is shown below.

Results of analysis of the brown powder obtained in Step 3 by nuclearmagnetic resonance spectrometry (¹H-NMR) are shown below. FIG. 6 is the¹H-NMR chart. The results demonstrate that [Ir(dmdpq)₂(dpm)], which isthe organometallic iridium complex of one embodiment of the presentinvention and is represented by Structural Formula (100), was obtainedin Synthesis Example 1.

¹H-NMR. δ (CDCl₃): 0.77 (s, 18H), 1.07 (s, 6H), 2.00 (s, 6H), 2.46 (s,12H), 4.85 (s, 1H), 6.42 (s, 2H), 7.01 (s, 2H), 7.22 (s, 2H), 7.38 (t,2H), 7.57 (t, 2H), 7.72 (s, 4H), 7.94 (d, 2H), 8.02 (d, 2H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an absorption spectrum) and an emission spectrum of[Ir(dmdpq)₂(dpm)] in a dichloromethane solution were measured. Theabsorption spectrum was measured with an ultraviolet-visible lightspectrophotometer (V550 type, produced by JASCO Corporation) at roomtemperature in the state where the dichloromethane solution (0.063mmol/L) was in a quartz cell. In addition, the measurement of theemission spectrum was conducted at room temperature, for which afluorescence spectrophotometer (FS920 manufactured by HamamatsuPhotonics K.K.) was used and the degassed dichloromethane solution(0.063 mmol/L) was put in a quartz cell. FIG. 7 shows measurementresults of the absorption spectrum and emission spectrum. The horizontalaxis represents wavelength and the vertical axes represent absorptionintensity and emission intensity. In FIG. 7, two solid lines are shown:a thin line represents the absorption spectrum, and a thick linerepresents the emission spectrum. The absorption spectrum shown in FIG.7 was obtained by subtraction of the absorption spectra of thedichloromethane and the quartz from the obtained absorption spectrum.

As shown in FIG. 7, [Ir(dmdpq)₂(dpm)] that is the organometallic iridiumcomplex of one embodiment of the present invention has an absorptionpeak at 475 nm and an emission peak at 722 nm. In addition, deep redlight emission was observed in the dichloromethane solution.

Next, [Ir(dmdpq)₂(dpm)] obtained in this example was subjected to a MSanalysis by liquid chromatography mass spectrometry (LC-MS).

In the LC-MS, liquid chromatography (LC) separation was carried out withACQUITY UPLC (manufactured by Waters Corporation) and mass spectrometry(MS) was carried out with Xevo G2 Tof MS (manufactured by WatersCorporation). ACQUITY UPLC BEH C8 (2.1×100 mm, 1.7 μm) was used as acolumn for the LC separation, and the column temperature was 40° C.Acetonitrile was used for Mobile Phase A and a 0.1% aqueous solution offormic acid was used for Mobile Phase B. A sample was prepared in such amanner that [Ir(dmdpq)₂(dpm)] was dissolved in toluene at a givenconcentration and the solution was diluted with acetonitrile. Theinjection amount was 5.0 μL.

In the MS analysis, ionization was carried out by an electrosprayionization (abbreviation: ESI) method. At this time, the capillaryvoltage and the sample cone voltage were set to 3.0 kV and 30 V,respectively, and detection was performed in a positive mode. All thecomponents that were ionized under the above conditions were collidedwith an argon gas in a collision cell to dissociate into product ions.Energy (collision energy) for the collision with argon was 30 eV. A massrange for the measurement was m/z=100-1120. The detection results of thegenerated product ions by time-of-flight (TOF) MS are shown in FIG. 8.

The results in FIG. 8 demonstrate that product ions of[Ir(dmdpq)₂(dpm)], which is one embodiment of the present invention andis represented by Structural Formula (100), were detected mainly aroundm/z=867 and around m/z=339. The results in FIG. 8 are characteristicallyderived from [Ir(dmdpq)₂(dpm)] and can thus be regarded as importantdata in identification of [Ir(dmdpq)₂(dpm)] contained in a mixture.

It is presumed that the product ion around m/z=867 is a cation in astate where dipivaloylmethane and a proton were eliminated from thecompound represented by Structural Formula (100), and this is acharacteristic of the organometallic iridium complex of one embodimentof the present invention. In addition, it is presumed that the production around m/z=339 is a cation in a state where a proton was added tothe quinoxaline derivative Hdmdpq, and this indicates a structure of[Ir(dmdpq)₂(dpm)] that is the organometallic iridium complex of oneembodiment of the present invention.

Furthermore, in this embodiment, it was examined whether the emissionwavelength (peak wavelength) of an organometallic iridium complex thathas a structure in which a phenyl group that is bonded to a quinoxalineskeleton and bonded to iridium has two substituents that are any of analkyl group having 1 to 6 carbon atoms, a phenyl group, and a phenylgroup having an alkyl group having 1 to 6 carbon atoms as a substituentand the two substituents are bonded to the 4-position and the 6-positionof the phenyl group bonded to iridium is longer than the emissionwavelength of an organometallic iridium complex that does not have suchsubstituents.

Specifically, emission spectra of the following two organometalliciridium complexes were measured: the organometallic iridium complex[Ir(dmdpq)₂(dpm)] described in this example, that is, the organometalliciridium complex having a structure in which a phenyl group that isbonded to a quinoxaline skeleton and bonded to iridium has twosubstituents (methyl groups) at the 4-position and the 6-position, andan organometallic iridium complex [Ir(dpq)₂(acac)], that is, anorganometallic iridium complex having a structure in which a phenylgroup that is bonded to a quinoxaline skeleton and bonded to iridiumdoes not have such substituents. Structural formulae of the two measuredorganometallic iridium complexes are shown below.

The emission spectra were measured by the above-described method. FIG.12 shows the measurement results. The measurement results confirm thatthe emission wavelength of [Ir(dmdpq)₂(dpm)] that is one embodiment ofthe present invention is longer by approximately 50 nm than the emissionwavelength of [Ir(dpq)₂(acac)] that has the structure in which thephenyl group that is bonded to the quinoxaline skeleton and bonded toiridium does not have the substituents.

Therefore, the results demonstrate that [Ir(dmdpq)₂(dpm)] that is oneembodiment of the present invention is a novel organometallic iridiumcomplex that emits near-infrared light (emission wavelength: around 700nm).

Example 2 Synthesis Example 2

In this example, a method of synthesizingbis[4,6-dimethyl-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium(III) (abbreviation: [Ir(mdmpq)₂(acac)]) that is anorganometallic iridium complex of one embodiment of the presentinvention and is represented by Structural Formula (114) in Embodiment 1is described. A structure of [Ir(mdmpq)₂(acac)] is shown below.

Step 1: Synthesis of 2-(3,5-dimethylphenyl)-3-methylquinoxaline(Abbreviation: Hmdmpq)

First, 3.02 g of 2-chloro-3-methylquinoxaline, 3.88 g of3,5-dimethylphenyl boronic acid, 2.77 g of sodium carbonate, 0.14 g ofbis(triphenylphosphine)palladium(II)dichloride (abbreviation:Pd(PPh₃)₂Cl₂), 20 mL of water, and 20 mL of DMF were put in a recoveryflask equipped with a reflux pipe, and the air in the flask was replacedwith argon. Heating was performed by irradiation with microwaves (2.45GHz, 100 W) for 2 hours. Then, water was added to this solution, and theorganic layer was extracted with dichloromethane. The obtained organiclayer was washed with water and saturated saline, and was dried withmagnesium sulfate. The solution obtained by the drying was filtered. Thesolvent of this solution was distilled off, and the obtained residue waspurified by flash column chromatography using hexane and ethyl acetatein a volume ratio of 5:1 as a developing solvent. The solid obtained byconcentration of a fraction was purified by flash column chromatographyusing dichloromethane as a developing solvent to give a targetquinoxaline derivative, Hmdmpq, as flesh color powder in a yield of 72%.Note that the irradiation with microwaves was performed using amicrowave synthesis system (Discover, manufactured by CEM Corporation).Synthesis Scheme (b-1) of Step 1 is shown below.

Step 2: Synthesis ofdi-μ-chloro-tetrakis[4,6-dimethyl-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC]diiridium(III)(Abbreviation: [Ir(mdmpq)₂Cl]₂)

Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.00 g of Hmdmpq obtainedin Step 1, and 0.57 g of iridium chloride hydrate (IrCl₃.H₂O) (producedby Sigma-Aldrich Corporation) were put in a recovery flask equipped witha reflux pipe, and the air in the flask was replaced with argon. Afterthat, irradiation with microwaves (2.45 GHz, 100 W) was performed for 1hour to cause a reaction. The solvent was distilled off, and then theobtained residue was suction-filtered and washed with ethanol to give adinuclear complex, [Ir(mdmpq)₂Cl]₂, as brown powder in a yield of 62%.Synthesis Scheme (b-2) of Step 2 is shown below.

Step 3: Synthesis ofbis[4,6-dimethyl-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium (III) (Abbreviation: [Ir(mdmpq)₂(acac)])

Furthermore, 30 mL of 2-ethoxyethanol, 0.86 g of the Binuclear complex,[Ir(mdmpq)₂Cl]₂, obtained in Step 2, 0.18 g of acetylacetone(abbreviation: Hacac), and 0.64 g of sodium carbonate were put in arecovery flask equipped with a reflux pipe, and the air in the flask wasreplaced with argon. After that, the flask was subjected to irradiationwith microwaves (2.45 GHz, 120 W) for 60 minutes to be heated. Here,0.18 g of Hacac was further added, and heating was performed byirradiation with microwaves (2.45 GHz, 120 W) for 60 minutes. Water wasadded to the reacted solution and the organic layer was extracted withdichloromethane. The obtained organic layer was washed with water andsaturated saline, and was dried with magnesium sulfate. The solutionobtained by the drying was filtered. The solvent of this solution wasdistilled off, and the obtained residue was purified by flash columnchromatography using hexane and ethyl acetate in a volume ratio of 5:1as a developing solvent to give [Ir(mdmpq)₂(acac)], which is theorganometallic iridium complex of one embodiment of the presentinvention, as black powder in a yield of 9%. Synthesis Scheme (b-3) ofStep 3 is shown below.

Results of analysis of the black powder obtained by the above-describedsynthesis method by nuclear magnetic resonance spectrometry (¹H-NMR) areshown below. FIG. 9 is the ¹H-NMR chart. The results demonstrate that[Ir(mdmpq)₂(acac)], which is the organometallic iridium complex of oneembodiment of the present invention and is represented by StructuralFormula (114), was obtained in Synthesis Example 2.

¹H-NMR. δ (CDCl₃): 1.23 (s, 6H), 1.29 (s, 6H), 2.40 (s, 6H), 3.34 (s,6H), 4.23 (s, 1H), 6.63 (s, 2H), 7.33 (t, 2H), 7.53 (t, 2H), 7.65 (d,2H), 7.90 (d, 2H), 7.94 (s, 2H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an absorption spectrum) and an emission spectrum of[Ir(mdmpq)₂(acac)] in a dichloromethane solution were measured. Theabsorption spectrum was measured with an ultraviolet-visible lightspectrophotometer (V550 type, produced by JASCO Corporation) at roomtemperature in the state where the dichloromethane solution (0.089mmol/L) was in a quartz cell. In addition, the measurement of theemission spectrum was conducted at room temperature, for which afluorescence spectrophotometer (FS920 manufactured by HamamatsuPhotonics K.K.) was used and the degassed dichloromethane solution(0.089 mmol/L) was put in a quartz cell. FIG. 10 shows measurementresults of the absorption spectrum and emission spectrum. The horizontalaxis represents wavelength and the vertical axes represent absorptionintensity and emission intensity. In FIG. 10, two solid lines are shown:a thin line represents the absorption spectrum, and a thick linerepresents the emission spectrum. The absorption spectrum shown in FIG.10 was obtained by subtraction of the absorption spectra of thedichloromethane and the quartz from the obtained absorption spectrum.

As shown in FIG. 10, [Ir(mdmpq)₂(acac)] that is the organometalliciridium complex of one embodiment of the present invention has anabsorption peak at 470 nm and an emission peak at 706 nm. In addition,deep red light emission was observed in the dichloromethane solution.

Next, [Ir(mdmpq)₂(acac)] obtained in this example was subjected to a MSanalysis by liquid chromatography mass spectrometry (LC-MS).

In the LC-MS, liquid chromatography (LC) separation was carried out withACQUITY UPLC (manufactured by Waters Corporation) and mass spectrometry(MS) was carried out with Xevo G2 Tof MS (manufactured by WatersCorporation). ACQUITY UPLC BEH C8 (2.1×100 mm, 1.7 μm) was used as acolumn for the LC separation, and the column temperature was 40° C.Acetonitrile was used for Mobile Phase A and a 0.1% aqueous solution offormic acid was used for Mobile Phase B. A sample was prepared in such amanner that [Ir(mdmpq)₂(acac)] was dissolved in toluene at a givenconcentration and the solution was diluted with acetonitrile. Theinjection amount was 5.0 μL.

In the MS analysis, ionization was carried out by an electrosprayionization (abbreviation: ESI) method. At this time, the capillaryvoltage and the sample cone voltage were set to 3.0 kV and 30 V,respectively, and detection was performed in a positive mode. All thecomponents that were ionized under the above conditions were collidedwith an argon gas in a collision cell to dissociate into product ions.Energy (collision energy) for the collision with argon was 50 eV. A massrange for the measurement was m/z=100−1200. The detection results of thegenerated product ions by time-of-flight (TOF) MS are shown in FIG. 11.

The results in FIG. 11 demonstrate that product ions of[Ir(mdmpq)₂(acac)], which is one embodiment of the present invention andis represented by Structural Formula (114), were detected mainly aroundm/z=679, around m/z=539, and around m/z=437. The results in FIG. 11 arecharacteristically derived from [Ir(mdmpq)₂(acac)] and can thus beregarded as important data in identification of [Ir(mdmpq)₂(acac)]contained in a mixture.

It is presumed that the product ion around m/z=679 is a cation in astate where acetylacetone and a proton were eliminated from the compoundrepresented by Structural Formula (114), and this is a characteristic ofthe organometallic iridium complex of one embodiment of the presentinvention. In addition, it is presumed that the product ion aroundm/z=539 is a cation in a state where the quinoxaline derivative Hmdmpqwas eliminated from the compound represented by Structural Formula (114)and that the product ion around m/z=437 is a cation in a state whereacetylacetone and a proton were eliminated from the product ionaround=m/z 539, which indicates a structure of [Ir(mdmpq)₂(acac)] thatis the organometallic iridium complex of one embodiment of the presentinvention.

Furthermore, in this embodiment, it was examined whether the emissionwavelength (peak wavelength) of an organometallic iridium complex thathas a structure in which a phenyl group that is bonded to a quinoxalineskeleton and bonded to iridium has two substituents that are any of analkyl group having 1 to 6 carbon atoms, a phenyl group, and a phenylgroup having an alkyl group having 1 to 6 carbon atoms as a substituentand the two substituents are bonded to the 4-position and the 6-positionof the phenyl group bonded to iridium is longer than the emissionwavelength of an organometallic iridium complex that does not have suchsubstituents.

Specifically, emission spectra of the following two organometalliciridium complexes were measured: the organometallic iridium complex[Ir(mdmpq)₂(acac)] described in this example, that is the organometalliciridium complex having a structure in which a phenyl group that isbonded to a quinoxaline skeleton and bonded to iridium has twosubstituents (methyl groups) at the 4-position and the 6-position, andan organometallic iridium complex [Ir(mpq)₂(acac)], that is, anorganometallic iridium complex having a structure in which a phenylgroup that is bonded to a quinoxaline skeleton and bonded to iridiumdoes not have such substituents. Structural formulae of the two measuredorganometallic iridium complexes are shown below.

The emission spectra were measured by the above-described method. FIG.13 shows the measurement results. The measurement results confirm thatthe emission wavelength of [Ir(mdmpq)₂(acac)] that is one embodiment ofthe present invention is longer by approximately 50 nm than the emissionwavelength of [Ir(mpq)₂(acac)] that has the structure in which thephenyl group that is bonded to the quinoxaline skeleton and bonded toiridium does not have the substituents.

Therefore, the results demonstrate that [Ir(mdmpq)₂(acac)] that is oneembodiment of the present invention is a novel organometallic iridiumcomplex that emits near-infrared light (emission wavelength: around 700nm).

Example 3 Synthesis Example 3

In this example, a method of synthesizingbis[4,6-bis(2-methylpropyl)-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(mdiBupq)₂(acac)]) that is an organometallic iridiumcomplex of one embodiment of the present invention and is represented byStructural Formula (118) in Embodiment 1 is described. A structure of[Ir(mdiBupq)₂(acac)] is shown below.

Step 1: Synthesis of 2-(3,5-dichlorophenyl)-3-methylquinoxaline

First, 1.00 g of 2-chloro-3-methylquinoxaline, 0.84 g of3,5-dichlorophenyl boronic acid, 1.68 g of potassium carbonate, 0.049 gof tri(o-tolyl)phosphine, 20 mL of toluene, 5 mL of ethanol, and 6 mL ofwater were put in a three-neck flask equipped with a reflux pipe, andthe air in the flask was replaced with nitrogen. The inside of the flaskwas degassed under reduced pressure, 0.018 g of palladium acetate wasadded thereto, and the mixture was heated at 80° C. for 19 hours. Then,water was added to this solution, and the organic layer was extractedwith toluene. The obtained organic layer was washed with water andsaturated saline, and was dried with magnesium sulfate. The solutionobtained by the drying was filtered. The solvent of this solution wasdistilled off, and then the obtained residue was purified by flashcolumn chromatography using hexane and ethyl acetate in a volume ratioof 5:1 as a developing solvent to give a target quinoxaline derivativeas pale pink powder in a yield of 67%). Synthesis Scheme (c-1) of Step 1is shown below.

Step 2: Synthesis of2-[3,5-bis(2-methylpropyl)phenyl]-3-methylquinoxaline (Abbreviation:HmdiBupq)

Next, 0.76 g of 2-(3,5-dichlorophenyl)-3-methylquinoxaline obtained inStep 1, 1.00 g of (2-methylpropyl)boronic acid, 2.09 g of tripotassiumphosphate, 0.041 g of 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl(abbreviation: S-Phos), and 45 mL of toluene were put in a three-neckflask equipped with a reflux pipe, and the air in the flask was replacedwith nitrogen. The inside of the flask was degassed under reducedpressure, 0.024 g of tris(dibenzylideneacetone)dipalladium(0) was addedthereto, and the mixture was refluxed for 6.5 hours. Then, water wasadded to this solution, and the organic layer was extracted withtoluene. The obtained organic layer was washed with water and saturatedsaline, and was dried with magnesium sulfate. The solution obtained bythe drying was filtered. This solution was filtered through a filter aidin which Celite, alumina, and Celite were stacked in this order and thetoluene solvent was distilled off to give a target quinoxalinederivative HmdiBupq as orange oil in a yield of 82%. Synthesis Scheme(c-2) of Step 2 is shown below.

Step 3: Synthesis ofdi-μ-chloro-tetrakis[4,6-bis(2-methylpropyl)-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC]diiridium(III)(Abbreviation: [Ir(mdiBupq)₂Cl]₂)

Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.75 g of HmdiBupqobtained in Step 2, and 0.80 g of iridium chloride hydrate (IrCl₃.H₂O)(produced by Sigma-Aldrich Corporation) were put in a recovery flaskequipped with a reflux pipe, and the air in the flask was replaced withargon. After that, irradiation with microwaves (2.45 GHz, 100 W) wasperformed for 1 hour to cause a reaction. The solvent was distilled off,and then the obtained residue was suction-filtered and washed withhexane to give a Binuclear complex [Ir(mdiBupq)₂Cl]₂ as brown powder ina yield of 71%. Synthetic Scheme (c-3) of Step 3 is shown below.

Step 4: Synthesis ofbis[4,6-bis(2-methylpropyl)-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC](2,4-pentadionato-κ²O,O′)iridium(III)(Abbreviation: [Ir(mdiBupq)₂(acac)])

Furthermore, 30 mL of 2-ethoxyethanol, 2.32 g of the dinuclear complex[Ir(mdiBupq)₂Cl]₂ obtained in Step 3, 0.39 g of acetylacetone(abbreviation: Hacac), and 1.41 g of sodium carbonate were put in arecovery flask equipped with a reflux pipe, and the air in the flask wasreplaced with argon. After that, the flask was subjected to irradiationwith microwaves (2.45 GHz, 120 W) for 60 minutes to be heated. Here,0.39 g of Hacac was further added, and heating was performed byirradiation with microwaves (2.45 GHz, 200 W) for 60 minutes. Water wasadded to this solution, and the organic layer was extracted withdichloromethane. The obtained organic layer was washed with water andsaturated saline, and was dried with magnesium sulfate. The solutionobtained by the drying was filtered. The solvent of this solution wasdistilled off. The obtained residue was purified by flash columnchromatography using dichloromethane as a developing solvent andrecrystallized with a mixed solvent of dichloromethane and methanol togive [Ir(mdiBupq)₂(acac)], which is the organometallic iridium complexof one embodiment of the present invention, as black powder in a yieldof 4%. Synthesis Scheme (c-4) of Step 4 is shown below.

Results of analysis of the black powder obtained by the above-describedsynthesis method by nuclear magnetic resonance spectrometry (¹H-NMR) areshown below. FIG. 14 is the ¹H-NMR chart. The results demonstrate that[Ir(mdiBupq)₂(acac)], which is the organometallic iridium complex of oneembodiment of the present invention and is represented by StructuralFormula (118), was obtained in Synthesis Example 3.

¹H-NMR. δ (CDCl₃): −0.06 (d, 6H), 0.15 (d, 6H), 0.74-0.79 (m, 2H), 0.89(d, 12H), 1.25 (s, 6H), 1.35-1.39 (m, 2H), 1.48-1.52 (m, 2H), 1.83-1.89(m, 2H), 2.44-2.48 (m, 2H), 2.55-2.60 (m, 2H), 3.28 (s, 6H), 4.29 (s,1H), 6.54 (s, 2H), 7.44 (t, 2H), 7.53 (d, 2H), 7.63 (t, 2H), 7.93 (d,2H), 7.96 (s, 2H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an absorption spectrum) and an emission spectrum of[Ir(mdiBupq)₂(acac)] in a dichloromethane solution were measured. Theabsorption spectrum was measured with an ultraviolet-visible lightspectrophotometer (V550 type, produced by JASCO Corporation) at roomtemperature in the state where the dichloromethane solution (0.070mmol/L) was in a quartz cell. In addition, the measurement of theemission spectrum was conducted at room temperature, for which afluorescence spectrophotometer (FS920 manufactured by HamamatsuPhotonics K.K.) was used and the degassed dichloromethane solution(0.070 mmol/L) was put in a quartz cell. FIG. 15 shows measurementresults of the absorption spectrum and emission spectrum. The horizontalaxis represents wavelength and the vertical axes represent absorptionintensity and emission intensity. In FIG. 15, two solid lines are shown:a thin line represents the absorption spectrum, and a thick linerepresents the emission spectrum. The absorption spectrum shown in FIG.15 was obtained by subtraction of the absorption spectra of thedichloromethane and the quartz from the obtained absorption spectrum.

As shown in FIG. 15, [Ir(mdiBupq)₂(acac)] that is the organometalliciridium complex of one embodiment of the present invention has anabsorption peak at 473 nm and an emission peak at 706 nm. In addition,deep red light emission was observed in the dichloromethane solution.

Furthermore, in this embodiment, it was examined whether the emissionwavelength (peak wavelength) of an organometallic iridium complex thathas a structure in which a phenyl group that is bonded to a quinoxalineskeleton and bonded to iridium has two substituents that are any of analkyl group having 1 to 6 carbon atoms, a phenyl group, and a phenylgroup having an alkyl group having 1 to 6 carbon atoms as a substituentand the two substituents are bonded to the 4-position and the 6-positionof the phenyl group bonded to iridium is longer than the emissionwavelength of an organometallic iridium complex that does not have suchsubstituents.

Specifically, emission spectra of the following two organometalliciridium complexes were measured: the organometallic iridium complex[Ir(mdiBupq)₂(acac)] described in this example, that is theorganometallic iridium complex having a structure in which a phenylgroup that is bonded to a quinoxaline skeleton and bonded to iridium hastwo substituents (methyl groups) at the 4-position and the 6-position,and an organometallic iridium complex [Ir(mpq)₂(acac)], that is, anorganometallic iridium complex having a structure in which a phenylgroup that is bonded to a quinoxaline skeleton and bonded to iridiumdoes not have such substituents. Structural formulae of the two measuredorganometallic iridium complexes are shown below.

The emission spectra were measured by the above-described method. FIG.16 shows the measurement results. The measurement results confirm thatthe emission wavelength of [Ir(mdiBupq)₂(acac)] that is one embodimentof the present invention is longer by approximately 50 nm than theemission wavelength of [Ir(mpq)₂(acac)] that has the structure in whichthe phenyl group that is bonded to the quinoxaline skeleton and bondedto iridium does not have the substituents.

Therefore, the results demonstrate that [Ir(mdiBupq)₂(acac)] that is oneembodiment of the present invention is a novel organometallic iridiumcomplex that emits near-infrared light (emission wavelength: around 700nm).

Example 4

In this example, a light-emitting element 1 in which [Ir(dmdpq)₂(dpm)](Structural Formula (100)) that is the organometallic iridium complex ofone embodiment of the present invention was used in a light-emittinglayer, a light-emitting element 2 in which [Ir(mdmpq)₂(acac)](Structural Formula (114)) that is the organometallic iridium complex ofone embodiment of the present invention was used in a light-emittinglayer, and a light-emitting element 3 in which [Ir(mdiBupq)₂(acac)](Structural Formula (118)) that is the organometallic iridium complex ofone embodiment of the present invention was used in a light-emittinglayer were fabricated, and emission spectra of the light-emittingelements were measured. Note that the fabrication of each of thelight-emitting element 1, the light-emitting element 2, and thelight-emitting element 3 is described with reference to FIG. 17.Chemical formulae of materials used in this example are shown below.

<<Fabrication of Light-Emitting Element 1, Light-Emitting Element 2, andLight-Emitting Element 3>>

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 1100 by a sputtering method, so that a firstelectrode 1101 functioning as an anode was formed. The thickness of thefirst electrode 1101 was 110 nm. The electrode area was 2 mm×2 mm.

Next, as pretreatment for forming each of the light-emitting elements 1to 3 over the substrate 1100, the surface of the substrate was washed,baked at 200° C. for 1 hour, and subjected to UV ozone treatment for 370seconds

After that, the substrate 1100 was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate 1100was cooled down for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 1100 over whichthe first electrode 1101 was formed faced downward. In this example, acase is described in which a hole-injection layer 1111, a hole-transportlayer 1112, a light-emitting layer 1113, an electron-transport layer1114, and an electron-injection layer 1115, which are included in an ELlayer 1102, are sequentially formed by a vacuum evaporation method.

After reducing the pressure in the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were deposited by co-evaporation so that the massratio of DBT3P-II (abbreviation) to molybdenum oxide was 4:2, wherebythe hole-injection layer 1111 was formed over the first electrode 1101.The thickness of the hole-injection layer 1111 was 20 nm. Note that theco-evaporation is an evaporation method in which a plurality ofdifferent substances are vaporized from the respective evaporationsources at the same time.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was deposited by evaporation to a thickness of 20 nm, wherebythe hole-transport layer 1112 was formed.

Next, the light-emitting layer 1113 was formed on the hole-transportlayer 1112. In the case of the light-emitting element1,2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), andbis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-2-quinoxalinyl-κN]phenyl-κC}(2,2′,6,6′-tetramethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdpq)₂(dpm)]) were deposited by co-evaporation sothat the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(dmdpq)₂(dpm)]was 0.8:0.2:0.05. The thickness of the light-emitting layer 1113 in thelight-emitting element 1 was 40 nm.

In the case of the light-emitting element 2, 2mDBTBPDBq-II, PCBBiF, andbis[4,6-dimethyl-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(mdmpq)₂(acac)]) were deposited by co-evaporation sothat the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(mdmpq)₂(acac)]was 0.8:0.2:0.05. The thickness of the light-emitting layer 1113 in thelight-emitting element 2 was 40 nm.

In the case of the light-emitting element 3, 2mDBTBPDBq-II, PCBBiF, andbis[4,6-bis(2-methylpropyl)-2-(3-methyl-2-quinoxalinyl-κN)phenyl-κC](2,4-pentadionato-κ²O,O′)iridium(III)(abbreviation: [Ir(mdiBupq)₂(acac)]) were deposited by co-evaporation sothat the weight ratio of 2mDBTBPDBq-II to PCBBiF and[Ir(mdiBupq)₂(acac)] was 0.8:0.2:0.05. The thickness of thelight-emitting layer 1113 in the light-emitting element 3 was 40 nm.

Then, on the light-emitting layer 1113, 2mDBTBPDBq-II was deposited byevaporation to a thickness of 20 nm and then bathophenanthroline(abbreviation: Bphen) was deposited by evaporation to a thickness of 10nm, whereby the electron-transport layer 1114 was formed. Furthermore,lithium fluoride was deposited by evaporation to a thickness of 1 nm onthe electron-transport layer 1114, whereby the electron-injection layer1115 was formed.

Finally, aluminum was deposited by evaporation to a thickness of 200 nmon the electron-injection layer 1115, whereby the second electrode 1103serving as a cathode was formed. Through the above-described steps, thelight-emitting elements 1 to 3 were fabricated. Note that in all theabove evaporation steps, evaporation was performed by aresistance-heating method.

Table 3 shows element structures of the light-emitting elements 1 to 3fabricated in the above-described manner.

TABLE 1 Hole- Light- Electron- First Hole-injection transport emittinginjection Second electrode layer layer layer Electron-transport layerlayer electrode Light-emitting ITSO DBT3P-II:MoOx BPAFLP * 2mDBTBPDBq-IIBphen LiF Al element 1 (110 nm) (4:2 20 nm) (20 nm) (20 nm) (10 nm) (1nm) (200 nm) Light-emitting ITSO DBT3P-II:MoOx BPAFLP ** 2mDBTBPDBq-IIBphen LiF Al element 2 (110 nm) (4:2 20 nm) (20 nm) (20 nm) (10 nm) (1nm) (200 nm) Light-emitting ITSO DBT3P-II:MoOx BPAFLP *** 2mDBTBPDBq-IIBphen LiF Al element 3 (110 nm) (4:2 20 nm) (20 nm) (20 nm) (10 nm) (1nm) (200 nm) * 2mDBTBPDBq-II:PCBBiF:[Ir(dmdpq)₂(dpm)] (0.8:0.2:0.05 40nm) ** 2mDBTBPDBq-II:PCBBiF:[Ir(mdmpq)₂(acac)] (0.8:0.2:0.05 40 nm) ***2mDBTBPDBq-II:PCBBiF:[Ir(mdiBupq)₂(acac)] (0.8:0.2:0.05 40 nm)

Furthermore, the fabricated light-emitting elements 1 to 3 were sealedin a glove box containing a nitrogen atmosphere so as not to be exposedto the air (specifically, a sealant was applied onto outer edges of theelements, and at the time of sealing, first, UV treatment was performedand then heat treatment was performed at 80° C. for 1 hour).

<<Emission Characteristics of Light-Emitting Element 1, Light-EmittingElement 2, and Light-Emitting Element 3>>

Emission characteristics of the fabricated light-emitting element 1,light-emitting element 2, and light-emitting element 3 were measured.

FIG. 18 shows emission spectra of the light-emitting elements 1 to 3that were obtained when current was applied to the light-emittingelements 1 to 3 at a current density of 25 mA/cm². As shown in FIG. 18,the emission spectrum of the light-emitting element 1 has a peak ataround 722 nm, which indicates that the peak is derived from emission ofthe organometallic iridium complex [Ir(dmdpq)₂(dpm)]. The emissionspectrum of the light-emitting element 2 has a peak at around 708 nm,which indicates that the peak is derived from emission of theorganometallic iridium complex [Ir(mdmpq)₂(acac)]. The emission spectrumof the light-emitting element 3 has a peak at around 702 nm, whichindicates that the peak is derived from emission of the organometalliciridium complex [Ir(mdiBupq)₂(acac)].

Thus, it was confirmed that emission from the organometallic iridiumcomplexes emitting near-infrared light (emission wavelength: 700 nm) wasobtained in all of the light-emitting elements. In other words, the useof the organometallic iridium complex of one embodiment of the presentinvention for a light-emitting element allows the light-emitting elementto have high emission efficiency and a long lifetime and emitsnear-infrared light (emission wavelength: around 700 nm).

Comparative Example

In this comparative example, it was examined whether or not a structurein which a phenyl group that is bonded to a skeleton that is not aquinoxaline skeleton and bonded to iridium has two substituents that areany of an alkyl group having 1 to 6 carbon atoms, a phenyl group, and aphenyl group having an alkyl group having 1 to 6 carbon atoms as asubstituent, and the two substituents are bonded to the 4-position andthe 6-position of the phenyl group bonded to iridium is effective inmaking the emission wavelength (peak wavelength) of an organometalliciridium complex having the structure longer than the emission wavelengthof an organometallic iridium complex that does not have suchsubstituents.

Specifically, emission spectra of the following two organometalliciridium complexes were measured: an organometallic iridium complex[Ir(tBudmppm)₂(acac)], that is an organometallic iridium complex havinga structure in which a phenyl group that is bonded to a pyrimidineskeleton and bonded to iridium has two substituents (methyl groups) atthe 4-position and the 6-position, and an organometallic iridium complex[Ir(tBuppm)₂(acac)], that is an organometallic iridium complex having astructure in which a phenyl group that is bonded to a pyrimidineskeleton and bonded to iridium does not have such substituents.Structural formulae of the two measured organometallic iridium complexesare shown below.

The emission spectra were each measured using a degassed dichloromethanesolution with a fluorescence spectrophotometer as in the above-describedmethod. FIG. 19 shows the measurement results. The measurement resultsconfirm that the emission wavelength of [Ir(tBudmppm)₂(acac)] that hasthe structure in which the phenyl group that is bonded to the pyrimidineskeleton and bonded to iridium has two substituents (methyl groups) atthe 4-position and the 6-position is slightly longer than the emissionwavelength of [Ir(tBuppm)₂(acac)] that has the structure in which thephenyl group that is bonded to the pyrimidine skeleton and bonded toiridium does not have such substituents.

Thus, the organometallic iridium complex of one embodiment of thepresent invention having the quinoxaline skeleton has the structure inwhich the phenyl group that is bonded to the quinoxaline skeleton andbonded to iridium has two substituents at the 4-position and the6-position, so that the emission wavelength of the organometalliciridium complex can be located on the long-wavelength side. In addition,this enables a novel organometallic iridium complex that emitsnear-infrared light (emission wavelength: around 700 nm) to be provided.

EXPLANATION OF REFERENCE

-   101: first electrode, 102: EL layer, 103: second electrode, 111:    hole-injection layer, 112: hole-transport layer, 113: light-emitting    layer, 114: electron-transport layer, 115: electron-injection layer,    116: charge-generation layer, 201: anode, 202: cathode, 203: EL    layer, 204: light-emitting layer, 205: phosphorescent compound, 206:    first organic compound, 207: second organic compound, 301: first    electrode, 302(1): first EL layer, 302(2): second EL layer,    302(n−1): (n−1)th EL layer, 302(n): n-th EL layer, 304: second    electrode, 305: charge-generation layer (I), 305(1): first    charge-generation layer (I), 305(2): second charge-generation layer    (I), 305(n−2): (n−2)-th charge-generation layer (I), 305(n−1):    (n−1)-th charge-generation layer (I), 401: element substrate, 402:    pixel portion, 403: driver circuit portion (source line driver    circuit), 404 a, 404 b: driver circuit portion (gate line driver    circuit), 405: sealant, 406: sealing substrate, 407: wiring, 408:    flexible printed circuit (FPC), 409: n-channel FET, 410: p-channel    FET, 411: switching FET. 412: current control FET, 413: first    electrode (anode), 414: insulator, 415: EL layer, 416: second    electrode (cathode), 417: light-emitting element, 418: space, 1100:    substrate, 1101: first electrode, 1102: EL layer, 1103: second    electrode, 1111: hole-injection layer, 1112: hole-transport layer,    1113: light-emitting layer, 1114: electron-transport layer, 1115:    electron-injection layer, 8001: lighting device, 8002: lighting    device, 8003: lighting device, and 8004: lighting device.

This application is based on Japanese Patent Application serial no.2013-125429 filed with the Japan Patent Office on Jun. 14, 2013, theentire contents of which are hereby incorporated by reference.

The invention claimed is:
 1. A compound represented by Formula (G1):

wherein: L represents a monoanionic ligand, R¹ and R² separatelyrepresent a methyl group, an ethyl group, an isobutyl group, or aneopentyl group, and R³ represents a methyl group, an ethyl group, anisobutyl group, a 3,5-dimethylphenyl group, a 2-methylphenyl group, a2,6-dimethylphenyl group, or a 3,5-diethylphenyl group.
 2. The compoundaccording to claim 1, wherein the monoanionic ligand is any of amonoanionic bidentate chelate ligand having a beta-diketone structure, amonoanionic bidentate chelate ligand having a carboxyl group, amonoanionic bidentate chelate ligand having a phenolic hydroxyl group,and a monoanionic bidentate chelate ligand in which two ligand elementsare both nitrogen.
 3. The compound according to claim 1, wherein: themonoanionic ligand is a ligand represented by any of Formulae (L1) to(L7):

R⁷¹ to R¹¹¹ separately represent hydrogen, a substituted orunsubstituted alkyl group having 1 to 6 carbon atoms, a halogen group, avinyl group, a substituted or unsubstituted haloalkyl group having 1 to6 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to6 carbon atoms, or a substituted or unsubstituted alkylthio group having1 to 6 carbon atoms, A¹ to A³ separately represent nitrogen, sp²hybridized carbon bonded to hydrogen, or sp² hybridized carbon having asubstituent, and the substituent represents an alkyl group having 1 to 6carbon atoms, a halogen group, a haloalkyl group having 1 to 6 carbonatoms, or a phenyl group.
 4. The compound according to claim 1, wherein:the compound is represented by Formula (G2):

and R⁴ and R⁵ separately represent hydrogen, a substituted orunsubstituted alkyl group having 1 to 6 carbon atoms, a halogen group, avinyl group, a substituted or unsubstituted haloalkyl group having 1 to6 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to6 carbon atoms, or a substituted or unsubstituted alkylthio group having1 to 6 carbon atoms.
 5. A light-emitting device comprising the compoundaccording to claim
 1. 6. A lighting device comprising the light-emittingdevice according to claim 5.